As the paywalls go up, so an era ends. "Of course we expect to see the numbers of unique users of our websites come down dramatically," says Rebekah Brooks, Rupert Murdoch's grand vizier at Wapping. "The industry is making the mistake of chasing millions of users by giving the audience more and more content for free – an obsession with traffic that just doesn't pay."

We must wait a few more weeks to see how Murdoch's walls fare as they ring the Times, Sunday Times and the rest. How "dramatic" is a mass exodus? How many readers, in her words, will prove "committed to and engaged with" the titles? But one issue brooks no waiting: the whole system of industry measurement online – via unique users, or, more accurately, browsers, clicking on every day – is shot as soon as News International walks away. It depends on consensual approval from newspapers and advertisers alike. Here's a unique depth charge.

Pretend that you're a top advertising executive with millions to spend in digital and print. Newspapers fawn on you. Online entrepreneurs worship at your laptop. But before placing an order, you need facts, figures, statistics that spell value for a client's money. At once things get murky.

The Audit Bureau of Circulations tells you how many actual copies of printed papers were sold, given away or lost in some black hole each month. But the whole impetus of the last few years has been to replicate that service online, now counting browser visits day by day so papers can put out combined statistics for copies sold and websites visited. Oh grandma, what big reach you've got!

Forget valiant distribution efforts and lorries stuck in snowdrifts. Once you're into ABCe figuring, the bureau's greatly slimmed ruling council is all about advertising executives seeking advertising facts: a shift in emphasis and personnel that automatically throws up questions of its own.

Where are these millions of unique browsers at home or around the globe? How long do they linger on your site? Maybe only a few minutes a month. Do they click on ads? Some 79%, on the latest Pew Center findings, say they've rarely, if ever, accessed an online ad. Progress, but still damnably spotty.

Perhaps the birth of the iPad will help. America's ABCs will start totting up visits there at once. But Murdoch's assault on this counting business tips over the board. Agencies are asking tougher questions about how effective printed ads are already: now the entire framework of industry-agreed monitoring online needs a fresh start.

And maybe it's happening. The National Readership Survey (NRS) – a giant opinion poll, not a counting of print copies – is a vital partner for ABC. It tells you what readers read, as opposed to how many issues they buy. It, too, is in the throes of change.

The idea involves recruiting a digital analysis giant (such as UKOM/Nielsen or Comscore) to provide details of online news site readership – time, intensity, age, gender, class – that will finally balance what the national survey does for print. In short, the complete package. Stack that alongside ABC's counting of copies, visits and clicks, and at last newspapers, online and off, will have a complete story to tell. "This is a major event for NRS," says Mike Ironside, its chief executive, "one that we believe will shape not only the future of the business but of media measurement as a whole."

Mission accomplished? Not yet. The biggest news sites on the internet, remember, aren't newspapers at all: they're Yahoo, Google, AOL and the rest. That competition shouts out for monitoring as well. And there's a litter of technical problems (like an inability to cope with Mac user figures) that need sorting along the way.

But, finally, things may be falling into place – not because Rebekah has built her paywall, but because she's helped blow up the old measurement markers. Finally, you'll discover which revenue streams flow and which don't: what reader engagement means. And then you can start to rebuild business models as well. Because measuring what works and what doesn't is where every new model begins.

■ Here's a simple equation (from the Pew Center's annual research on the state of journalism). One type of journalism is not shrinking: comment, analysis, and blogging are still on the rise.

What provides all the fuel for this comment? Eighty per cent of analysis goes back to reporting in the dear old "legacy media" (such as the New York Times). And what's happened to the number of people employed in reporting and editing on American papers over the last decade? A 30% capacity drop. So, more yack about fewer facts? That feels about right.